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Dead air on some external calls.

CUCM 6.1.1a

7962 phone w/8.3.3SR2 firmware

2811 voice gateway, MGCP.  12.4(15)T17 IOS (9.4.16 DSP version)

Have been trying to correct issue with dead air on calls or one-way audio, very few calls have this issue out of many and only the receptionist is reporting this problem.

The calls come in the 2811 MGCP gateway, go to Unity AA first then 0 out to receptionist. The gateway, Call Manager, Unity, and IP Phones are all on same IP subnet (VLAN).

I know the CUCM version is old but they also have call center and this has been working fine for quite awhile so before I just go updating stuff with current SRs/SUs I'd like to figure this out.

The gateway was on 12.4(15)T4 IOS when this was reported and I found a few DTMF bugs in that version they were experencing, and I upgraded the IOS on the gateway to 12.4(15)T17 and the problem calls has dropped by a lot but they still report a few a day. On the older 12.4(15)T4 IOS when the reception had a call with no audio they would say press 0 and the external caller would press 0 and then two way audio started working fine. Sometimes on the older IOS version the receptionist would hear a DTMF beep when they first picked up the call also. The DTMF bug ID in the older IOS version is

CSCso87127. Since the upgrade to 12.4(15)T17 that trick isn't working and the receptionist hasn't been hearing the DTMF beep on problem calls so making some progress on this but not out of woods yet.

I've looked over CUCM detailed traces of some problem calls and the traces show normal call setup with no errors or delays.

I haven't been able to duplicate the problem calls with several hundred calls yet. I've filled up the PRI on the 2811 and tested calls on all channels fine.

The receptionist's phone has been replaced also. I'm thinking of updating the 7962 to 8.5.2 firmware which is highest version compatible with 6.1 from the cisco documenation. The receptionist is also using attendant console but the calls ring into the phone directly (not through an attendant console pilot). 

Anyone seen this before?


Dead air on some external calls.

See if this helps,

Any of the following will be sufficient to get around this issue:

1. Configure the gateway for static payload type using the following commands

on the gateway:

mgcp behavior g729-variants static-pt

mgcp behavior dynamically-change-codec-pt disable

2. Disable g729br8 from being negotiated for this call. If CUCM is involved,

this is done with the service parameter "Strip G.729 Annex B (Silence

Suppression) from Capabilities".


Posted by WebUser Asad Raza from Cisco Support Community App

Dead air on some external calls.

Thanks for the ideas.

Trying a few other small things first and then will move on to that.

1) Disable second NIC on unity server not being used.

2) Disabled G729 on unity (not being used).

3) Upgraded phone firmware to latest compatible with 6.1, 8.5.2

Call Manager and the gateways have worked for years with no problem calls, unity crashed recently and was rebuilt so was trying to circle back and make sure nothing was missed which may be causing odd behaviors. A majority of the calls use unity as auto attendant.

Re: Dead air on some external calls.

Tried your MGCP ideas (still in place) and same problems on calls now and then.

Sent from Cisco Technical Support iPhone App

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